This document relates to Composite Right/Left Handed (CRLH) Metamaterial (MTM) antenna apparatus.
The propagation of electromagnetic waves in most materials obeys the right-hand rule for the (E,H,β) vector fields, which denotes the electrical field E, the magnetic field H, and the wave vector β (or propagation constant). The phase velocity direction is the same as the direction of the signal energy propagation (group velocity) and the refractive index is a positive number. Such materials are Right-Handed (RH) materials. Most natural materials are RH materials; artificial materials can also be RH materials.
A metamaterial is an artificial structure. When designed with a structural average unit cell size ρ much smaller than the wavelength of the electromagnetic energy guided by the metamaterial, the metamaterial behaves like a homogeneous medium to the guided electromagnetic energy. Unlike RH materials, a metamaterial may exhibit a negative refractive index, wherein the phase velocity direction is opposite to the direction of the signal energy propagation where the relative directions of the (E,H,β) vector fields follow a Left-Hand (LH) rule. Metamaterials that support only a negative index of refraction while at the same time having negative permittivity ∈ and negative permeability μ are referred to as pure LH metamaterials.
Many metamaterials are mixtures of LH metamaterials and RH materials and thus are CRLH metamaterials. A CRLH MTM can behave like an LH metamaterial at low frequencies and an RH material at high frequencies. Implementations and properties of various CRLH MTMs are described in, for example, Caloz and Itoh, “Electromagnetic Metamaterials: Transmission Line Theory and Microwave Applications,” John Wiley & Sons (2006). CRLH MTMs and their applications in antennas are described by Tatsuo Itoh in “Invited paper: Prospects for Metamaterials,” Electronics Letters, Vol. 40, No. 16 (August, 2004).
CRLH MTMs can be structured and engineered to exhibit electromagnetic properties that are tailored for specific applications and can be used in applications where it may be difficult, impractical or infeasible to use other materials. In addition, CRLH MTMs may be used to develop new applications and to construct new devices that may not be possible with RH materials.